Concrete Block Calculator
Written by Thierno Sadou Diallo, formula verified per our methodology • Last checked on 9/5/2026
The number of concrete blocks needed is calculated by multiplying the wall area by 10 (a standard 20×20×50 cm block covers 0.10 m² of wall), with a breakage margin. For a 10 × 1.80 m wall with a 5% margin, plan for 189 blocks.
Explanation
This calculator estimates the number of concrete blocks needed to build a rectangular wall, from its length and height. It relies on the most common trade rule for a standard block 20 cm high and 50 cm long (the most common dimensions in France): these two measurements conventionally include the thickness of the mortar joint, so a single block covers exactly 0.10 m² of wall, or 10 blocks per m². A breakage and cutting margin (5 to 10% depending on the wall's configuration) is added to make up for blocks broken during transport or laying, and the cuts needed at edges or corners. This calculator assumes a standard 20×20×50 cm block; for a different format (a 15 or 25 cm thick block, brick, another material), the number of blocks per m² changes accordingly, and this calculator doesn't directly apply. For the concrete volume of a slab rather than a block wall, see our concrete volume calculator.
Example: a 10 m long, 1.80 m high boundary wall
Inputs
Length: 10 m. Height: 1.80 m. Margin: 5%.
Calculation
Wall area = 10 × 1.80 = 18 m². Number of blocks = 18 × 10 × 1.05 = 189.
Result
You'll need to plan for 189 blocks for this wall.
Frequently asked questions
Why exactly 10 blocks per m²?
Because a standard block conventionally measures 50 cm long and 20 cm high (mortar joint included in both dimensions), so 0.50 × 0.20 = 0.10 m² of visible surface on the wall. One square meter divided by 0.10 m² gives exactly 10 blocks — a trade rule widely used for a quick first estimate.
Does this calculation account for openings (doors, windows)?
No, this calculator assumes a solid wall with no openings. For a wall with a door or window, calculate the opening's area separately (length × height) and subtract it from the total wall area before multiplying by 10, or remove the corresponding number of blocks from the final result.
Does this calculator include the mortar needed?
No, it only gives the number of blocks. The amount of laying mortar depends on the joint thickness and the coverage rate of the product used (ready-to-use mortar bags, or cement and sand mixed on site), which varies by manufacturer — refer to your chosen product's coverage specifications.